ADRENALIN / Four wheels good: Once just items of farmyard furniture, quads have found new favour with speed-hungry bikers. Joseph Gallivan reports

When a motorsport develops out of an agricultural activity you can guarantee one thing: it'll have a mental following. While motocross - rushing through mud on a motorbike with chunky tyres - has been around since bikes were invented, the rapidly growing sport of quad racing has put a spin on a recent piece of farm machinery, making the four-wheeler the home of a new generation of bikers who seek their thrills in the dirt.

Quads are four-wheeled ATVs (All Terrain Vehicles) which are powered by the same engines (250, 350 and 500cc, usually Japanese) found in motocross bikes. They cost around pounds 4,000 new, but a lot less used. A beginner can pick one up for a grand. On a farm they are just mini-tractors that leave less mess, but tuned up, re-geared and stripped of accessories they have become the perfect vehicle for 'maturing' motocross riders who are no longer fit enough to throw a bike around competitively.

On a windy Sunday in March at the disused aerodrome near Blyton, Lincolnshire, a hundred or so men, most in their early thirties, gather for a Nora (National Off Road Association) race meeting. In the ad hoc pits kneel riders and mechanics, oblivious to the cold, adjusting suspension, changing tyres, sprockets and chains, and, in some desperate cases, working on their carburettors.

Quads cannot be ridden on a public highway, but part of the thrill of racing these ATVs is their bizarre handling on asphalt. The best type of race is 70 per cent on 'tarmac', with incursions on to mud and man- made bumps and ramps. The steering also throws a bit of a curveball for the novice. Whereas on a motorbike you lean left when you're turning left, on a quad you go against instinct and lean to the right, so that your body weight keeps the offside wheels on the ground.

Racing, rather than fancy time-trials or skill events, is the whole point of quads. You line up in a grid system, revving like mad until the air is thick with the bitter smoke of synthetic two-stroke racing oil. On the flag, you flick the throttle open and let fly in first gear, praying the person in front doesn't stall.

Another reason why quads are banned from roads is the 'live' back axle, which means the power goes straight from the engine to the back axle by way of a chain. Imagine a small rocking horse with a rocket strapped to the back and you're approaching the feel of it.

You don't want to seize at 100mph on concrete wearing only flashy nylon trousers and a long sleeved T-shirt. Plans are afoot at Nora to make leathers compulsory, but, for the moment, quad racers are a motley crew mixing the sort of gear that wouldn't help if you fell off your skateboard with the odd scuffed biker jacket. 'Trouble is, soon as they get some money, lads spend it on new tyres or chains,' says Rob, one of the racers. 'Your body is an afterthought.'